I took 5 A Levels and 1 AS Level in the old UK system which seems similar to the CIE system. I didn’t find it particularly tough going. I mean, I managed to work part time, do a few hours of dance/swimming/sports, driving lessons etc so not like I did nothing but study!
Many universities require GCSEs in English and Maths if not offered at a higher level. So perhaps your school makes them compulsory if your earlier qualifications wouldn’t be easily recognised at international universities? Avoids the need to take IELTS type tests too.
Or have you already done IGCSEs?